The general possibility of polymer blends constituting interpenetrating polymer networks or IPN's has been known since 1969. Work in this field is summarized in the Encyclopedia of Polymer Science and Technology, Supplement Volume 1. The primary practical improvement obtained by the use of such IPN's has been increased toughness for plastics. However, no previous such compositions have been produced having the specific balance of properties required for use in the sealing and gasket operations as the present IPN's are directed.
A wide variety of natural and synthetic rubbers and other elastomers have previously been used for general sealing applications. For example, Japanese Appln. 59-213,786, teaches compositions comprising 100 parts by weight of urethane foam impregnated with 20-90 parts by weight of a mixture of a styrene-butadiene or styrene-isoprene block copolymer, bituminous material, an organic solvent, and optionally paraffinic or aromatic hydrocarbon oils, silicon water-repellents and/or defoaming agents, and inorganic fillers.
Japanese Appln. 58-215,334 discloses a "water-swelling sealant" comprising a rubber or plastic compound blended with a water-swelling polyurethane resin. The blend is mixed with an organic peroxide, molded or extruded to any desired shape, and then heated to 100.degree.-200.degree. C. to provide a water-swelling sealant.
Japanese Appln. 57-092,078 discloses a sealing material made by mixing a urethane polymer having a polydiene chain in the molecule and terminal isocyanate groups with an active hydrogen-containing compound and then curing the mixture by a urethane reaction to form the final elastomer.
U.S. Pat. No. 4,593,068 discloses a curing composition of a polyether having at least one reactive silicon-containing group in the molecule and an acrylate or methacrylate polymer. The product has substantial initial tackiness and is substantially non-elastomeric, even when large amounts of a plasticizer are added.
U.S. Pat. No. 3,642,936 discloses a non-extrudable, non-moldable coating composition for forming glossy vapor permeable finishes on natural leather and synthetic sheet material. Dissolved in a substantial amount of an organic solvent are an isocyanate-terminated polyurethane, a vinyl chloride polymer, and a reactive polysiloxane. The result is a useful flexible coating which is neither extrudable nor elastomeric.
It is an object of the present invention to produce compositions which, after hot-melt extrusion and before curing, (i) have sufficient melt strength to maintain the extruded shape in the substantial absence of sagging when extruded vertically, (ii) are alternatively initially tack-free or self-adhesive, and which, after curing by exposure to moisture, (iii) yields an elastomeric product which has an extremely low compression set, particularly at elevated temperature, and may be either foamed or essentially non-foamed.